Polydimethylsiloxane oils, particularly when formulated with a silica powder, are known for their ability to reduce frothing or foaming in aqueous systems. There are also examples in the art where organic formulations have been used to control foam in such systems. Such antifoaming or defoaming agents find utility in many industrial processes, some of which would be highly impractical were the agent not available.
Antifoam agents containing both organic and silicone components are also known in the art. For example, U.S. Pat. No. 3,959,175 to Smith et al. discloses a defoamer based on a mixture of polyisobutylene and a high melting hydrophobic component, such as fatty amide, fatty acid or tri-glyceride, or a mixture of the polyisobutylene and a hydrophobic material such as treated silica powder. Combination of the above three ingredients is also taught by Smith et al. This prior art patent incorrectly includes silicone oil as a member of the aforementioned "high melting" component which is said to have a melt point above 40.degree. C. (the typical melting point of a polydimethylsiloxane oil is actually about -40.degree. C.). This patent illustrates the invention with examples wherein silicone oil is used, albeit at levels of no more than 0.5 percent. The viscosity of the silicone oil used is not stated and no criticality thereof is suggested by Smith et al. Likewise, the polyisobutylene taught is shown to have particular end groups of the formula --CH.sub.2 C(CH.sub.3)=CH.sub.2, and there is no suggestion to alter this group.